cupoftea
Advanced Member level 6
Hi,
I was just diff probing a signal on the primary side of a 100W , 3 phase delta offline SMPS. It has a 3_coil common mode choke. It also has y capacitors to earth, upstream of the common mode choke. The signal was deluged by common mode noise, and not actually visible.
Then I added a y capacitor across the smps isolation transformer. And also a y cap downstream of each common mode choke coil to earth…so 4 extra y capacitors.
I could then see the signal really well, since adding the y capacitors cleaned up the noise.
But then I removed the earth connection to the SMPS….and still found the noise was cleaned up.
Would you expect this?
I was just diff probing a signal on the primary side of a 100W , 3 phase delta offline SMPS. It has a 3_coil common mode choke. It also has y capacitors to earth, upstream of the common mode choke. The signal was deluged by common mode noise, and not actually visible.
Then I added a y capacitor across the smps isolation transformer. And also a y cap downstream of each common mode choke coil to earth…so 4 extra y capacitors.
I could then see the signal really well, since adding the y capacitors cleaned up the noise.
But then I removed the earth connection to the SMPS….and still found the noise was cleaned up.
Would you expect this?